1. Field of the Invention
The present invention relates to a drum type washing machine that is capable of calculating the weight of laundry (hereinafter, also referred to as ‘laundry amount’) received in a drum and a program to calculate the laundry amount.
2. Description of the Related Art
To optimally set the amount of water necessary for respective processes of washing or the rotation speed of a drum, it is important to calculate laundry amount with high accuracy. In the past, an equation of motion was solved using voltage of a motor or rotational acceleration of a drum to calculate inertia on the drum and thus calculate the weight of laundry (Japanese Patent No. 3641581).
However, the voltage of the motor and the rotation speed of the drum used in the calculation method include an error due to a windage loss, a mechanical loss, an effect by contact friction between laundry articles, an effect by the fluctuation of power supply voltage or a load, an effect by the difference between machine bodies of washing machines due to bearing friction, and unbalance of laundry clinging to the drum, with the result that it is difficult to calculate laundry amount with high accuracy. Also, pulse measurement using a hole integrated circuit (IC) is generally performed to measure the rotation speed of the drum with low costs. In this case, however, a determination error may be generated due to the nonuniformity of the pulse.
For this reason, the measurement may be repeated several times to remove such an error factor and calculate laundry amount with high accuracy. In this case, however, the measurement may be carried out for a long time, and a resonance-related problem may occur.
Inventors of the present application proposed an invention that is capable of solving some of the above-mentioned problems, of which a patent application has been filed with the Japanese Patent Office and accorded Japanese Patent Application No. 2006-224117.
This invention discloses a method of calculating the weight of laundry considering a fact that the unbalance of laundry amount is dominant in the measurement error, particularly at a low-speed rotation. This method calculates inertia by an equation of motion using an average rotational acceleration during a period for which a drum makes one rotation, thereby canceling the effect of unbalance torque with respect to rotation speed generated due to the unbalance of laundry as shown in FIG. 1 and, at the same time, achieving the measurement of laundry amount within a short time without causing resonance.
More specifically, an equation of rotational motion related to a rotary drum considering the unbalance torque in the rotational direction due to the cling of laundry to the drum by the bias of the laundry may be represented by Equation 1 below.
                    [                  Equation          ⁢                                          ⁢          1                ]                                                                      T          +                      Mg            ⁢                                                  ⁢            sin            ⁢                                                  ⁢            ω            ⁢                                                  ⁢            t                          =                              J            ⁢                                          ⅆ                ω                                            ⅆ                t                                              +                      D            ⁢                                                  ⁢            ω                                              (        1        )            
Where, T is torque, M is unbalance, g is the acceleration of gravity, t is time, J is inertia, D is the coefficient of viscosity, and ω is rotation speed. The mechanical loss is omitted.
Opposite sides of Equation 1 are multiplied by dt and integrated with one rotation to obtain Equation 2.
                    [                  Equation          ⁢                                          ⁢          2                ]                                                                                  ∫                                          (                                  T                  +                                      Mg                    ⁢                                                                                  ⁢                    sin                    ⁢                                                                                  ⁢                    ω                    ⁢                                                                                  ⁢                    t                                                  )                            ⁢                              ⅆ                t                                              =                      ∫                                          (                                                      J                    ⁢                                                                  ⅆ                        ω                                                                    ⅆ                        t                                                                              +                                      D                    ⁢                                                                                  ⁢                    ω                                                  )                            ⁢                              ⅆ                t                                                    ⁢                                  ⁢                                            T              ⁢                                                          ⁢              Δ              ⁢                                                          ⁢              t                        +                          Mg              ⁢                                                ∫                  0                                      2                    ⁢                                                                                  ⁢                    π                                                  ⁢                                  sin                  ⁢                                                                          ⁢                  θ                  ⁢                                      ⅆ                    θ                                                                                =                                    J              ⁢                                                ∫                                      ω                    ⁢                                                                                  ⁢                    1                                                        ω                    ⁢                                                                                  ⁢                    2                                                  ⁢                                                      (                    1                    )                                    ⁢                                                                          ⁢                                      ⅆ                    ω                                                                        +                          D              ⁢                              ∫                                  ω                  ⁢                                                                          ⁢                                      ⅆ                                          ω                      ⁡                                              (                                                                              ⅆ                            t                                                                                ⅆ                            ω                                                                          )                                                                                                                                ⁢                                  ⁢                              T            ⁢                                                  ⁢            Δ            ⁢                                                  ⁢            t                    =                                    J              ⁢                                                          ⁢              Δ              ⁢                                                          ⁢              ω                        +                                          D                2                            ⁢                              (                                                      ω                    2                    2                                    -                                      ω                    1                    2                                                  )                            ⁢                                                Δ                  ⁢                                                                          ⁢                  t                                                  Δ                  ⁢                                                                          ⁢                  ω                                                                                        (        2        )            
Where, Δt is time required for one rotation, ω1 is initial speed, ω2 is final speed, and Δω is the change of speed during one rotation (Δω=ω2−ω1).
The existence of unbalance M is canceled through the integration with one rotation by Equation 1, and therefore, it can be seen that the effect of the unbalance of laundry with respect to torque is excluded from this calculation method.
Subsequently, Equation 2 is solved with respect to inertia J, and the torque is divided into normal operation torque τ and acceleration torque Δτ, such that T is expressed as τ+Δτ, to obtain Equation 3.
                    [                  Equation          ⁢                                          ⁢          3                ]                                                            J        =                                            (                              τ                +                Δτ                            )                        ⁢                                          Δ                ⁢                                                                  ⁢                t                                            Δ                ⁢                                                                  ⁢                ω                                              -                                    D              ⁡                              (                                                                            ω                      1                                                              Δ                      ⁢                                                                                          ⁢                      ω                                                        +                                      1                    2                                                  )                                      ⁢            Δ            ⁢                                                  ⁢            t                                              (        3        )            
Here, τ+Δτ is the amount of torque manipulated, and Δt, Δω, and ω1 are the amounts of change due to the acceleration measured. The coefficient of viscosity D may be uniformly maintained to calculate inertia H.
The above-mentioned invention is characterized by very accurate measurement of Δt and Δω. However, the initial speed ω1 included in Equation 3 changes due to unbalance M immediately before the start of acceleration, as shown in FIGS. 2 and 3, with the result that it is difficult to improve the accuracy in calculating the weight of laundry although the measurement is carried out merely several times to take an average.
To improve the accuracy in calculating the weight of laundry, it is necessary to uniformly maintain the initial speed ω1 every time of measurement. To uniformly maintain the initial speed ω1, it is necessary to uniformly control voltage V1 (equivalent to torque T) applied to the motor.
In practice, however, it is necessary to specify the position of the unbalance M of the laundry to equalize the initial speed ω1 and the voltage V1 immediately before every acceleration. Furthermore, many errors may be included in the calculation.